Fluid actuated down-hole drilling apparatus

ABSTRACT

A hydraulic drilling motor connectable to a drilling string of drill pipe thereabove and a drill bit therebelow for drilling a bore hole in the earth, the motor having a hollow rotor connected to a hollow drive shaft for attachment to the drill bit, the rotor being rotatable in a stator or housing fixed to the drilling string, the rotor passage being closed automatically by a valve when liquid or other fluid is pumped through the motor to produce rotor and shaft rotation, the valve automatically opening in the absence of pumping fluid through the motor to permit fluid to drain from the drilling string during its elevation with the motor in the bore hole, or to automatically fill with fluid during its lowering with the motor in the bore hole. Drilling weight is transferred from the non-rotating drilling string and housing to the drive shaft through an oil filled bearing section, the oil in such section being maintained at a higher pressure than the pressure externally of the section to retain the oil or other lubricant in a clean state.

limited States Patent [1 11] 3,840,080 Berryman 9 Oct. 8, 1974 1 FLUID ACTUATED DOWN-HOLE Primary Examiner-James A. Leppink DRILLING APPARATUS lnventor: William O. Berryman, Houston,

Tex.

[73] Assignee: Baker Oil Tools, Inc., Los Angeles,

Calif.

[22] Filed: Mar. 26, 1973 [21] Appl. No.: 345,094

[52] U.S. Cl. 175/107, 74/458 [51] Int. Cl E2lb 3/12 [58] Field of Search 175/107; 74/458 [56] References Cited UNITED STATES PATENTS 1,892,217- 12/1932 Moineau 74/458 2,250,912 7/1941 Hudson et a1. 2,890,859 6/1959 Garrison 3,112,801 12/1963 Clark et al. 175/107 3,603,407 9/1971 Clark 175/107 3,659,662 5/1972 Dicky 175/107 3,741,321 6/1973 Slouer, Jr. et a1. 175/107 Att0rney,'Agent, 0r Firm-Bernard Kriegel [57] ABSTRACT A hydraulic drilling motor connectable to a drilling string of drill pipe thereabove and a drill bit therebelow for drilling a bore hole in the earth, the motor having a hollow rotor connected to a hollow drive shaft for attachment to the drill bit, the rotor being rotatable in a stator or housing fixed to the drilling string, the rotor passage being closed automatically by a valve when liquid or other fluid is pumped through the motor to produce rotor and shaft rotation, the valve automatically opening in the absence of pumping fluid through the motor to permit fluid to drain from the drilling string during its elevation with the motor in the bore hole, or to automatically fill with fluid during its lowering with the motor in the bore hole. Drilling weight is transferred from the nonrotating drilling string and housing to the drive shaft through an oil filled bearing section, the oil in such section being maintained at a higher pressure than the pressure externally of the section to retain the oil or other lubricant in a clean state,

16 Claims, 11 Drawing Figures PATENTEDUET 8 m4 SKEW 30$ 3 .R IG. e,

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. r 1 FLUID ACTUATED DOWN-HOLE DRILLING APPARATUS The present invention relates to downhole drilling motor apparatus, and more particularly to hydraulic motor apparatus of the positive displacement type for attachment to a tubular drilling string for drilling straight or deviated bore holes in earth formations.

Downhole drilling motors of the positive displacement type are known, embodying a rotor and stator arrangement of the Moineau type illustrated and described in US. Pat. No. 1,892,217. The rotor in prior drilling motors has one lobe operating within a companion two lobe stator madeof rubber or corresponding elastomer material, the rotor itself being a solid steel member. The rotor partakes of an eccentric or orbital pass around the axis of the stator, producing an excessive amount of vibration as a result of the orbiting speed of the rotor, combined with its relatively high mass due to its solid construction, resulting in a decreased life of the rotor and of the parts of the motor associated therewith.

The drilling weight of prior motor apparatus is transmitted through a bearing assembly to the motor shaft, this bearing assembly being lubricated by the drilling mud or other fluid pumped down through the string of drill pipe and through the motor itself. Since drilling mud is very often sand laden, the bearings are operating in an abrasive liquid, resulting in their relatively short life, limiting the time that the apparatus can be used in drilling a bore hole, with consequent requirements for moving the entire motor apparatus from the bore hole and replacement of a substantial number of its parts, or, for that matter, replacement of the entire motor unit. Because of the use of the solid rotor, a dump valve assembly is incorporated in the drilling string above the motor to allow the drilling fluid to fill the drill pipe as the apparatus is run in the bore hole and to drain from the drill pipe while coming out of the hole.

The use of a single lobe rotor results in the rotor, drive shaft and bit connected thereto operating'at a relatively high speed, the motor being capable of producing a low maximum torque. Such high speed reduces considerably the drilling life of a drill bit, shortens the life of the bearings, and increases the aforementioned vibration difficulties. With a single lobe rotor, a limited fluid pressure differential can only be used to prevent excessive fluid slippage between the rotor and stator during orbital movement of the rotor around the stator axis, with consequent reduction in the horsepower developed by the drilling motor.

By virtue of the present invention, a downhold drilling motor is provided having a multiple lobe rotor operating within a companion multiple lobe stator. In a Moineau type of apparatus, the stator'has one lobe more than the rotor. With a drilling motor embodying a multiple lobe rotor, the pressure differential that can be used without an undesirable percentage of fluid slippage is far greater than with a single lobe rotor. Accordingly, for a given pressure differential, more drilling weight can be applied to the drilling bit, or, con versely, a given drilling weight can be applied to the bit with a less pressure drop across the drilling motor. Since the torque developed for a given pressureis much greater than in the prior drilling motors, and since. the pressure differential across the motor is greater, the combination of these factors results in the capability of the motor to generate a far greater torque than in the prior drilling motors. By way of example, since the torque generated at any pressure differential in applicants apparatus is about one and three-fourths times that developed by prior devices, the motor being operable at about twice the pressure differential of the prior devices, the motor of the present invention is capable of generating at least three and one-half times the torque of the prior devices. Accordingly, while drilling, the present apparatus has the capability of operating with about three. and one-half times as much drilling weight imposed on the drill bit.

With the present invention, the motor can develop the proper horsepower while operating at much slower speeds than prior fluid motors, permitting roller type drilling bits to be used without increased damage to their parts, so that the drilling bits are capable of drilling greater footages before requiring withdrawal from the bore hole and replacement. The result is a considerable saving in drilling cost per foot of hole, a lesser number of drilling bits being required for drilling a required length of bore hole, which is produced at greater drilling rates. Moreover, there is a substantial reduction in the time required for making round trips of the apparatus into and out of the bore hole for the purpose of changingdrilling bits.

By virtue of the present invention, the vibration of the rotor is considerably reduced by making it hollow, which reduces its mass, thereby contributing to long life of the motor and of the parts associated therewith. The vibration is also reduced by the ability to operate the drilling motor at reduced r.p.m.

Because of the use of a hollow rotor, with the advantages noted above, a dump valve assembly can be in- I corporated in the rotor itself, which is closed while drilling fluid is being pumped down through the drilling string and the drilling motor, but which automatically opens to permit the drilling mud or other fluid to drain from the drill pipe, through the hollow rotor, motor shaft and bit while the apparatus is being removed from a bore hole filled with drilling mud or other fluid, the string of drill pipe automatically filling with the drilling mud or other fluid in the bore hole while the drill pipe and apparatus are being run in the bore hole.

A further objective of the inventionv is to provide a bearing assembly in the drilling motor that is sealed against entry of external fluids and substances, such as the drilling mud, the bearing assembly being filled with oil maintained at a higher pressure than the pressure externally of the bearing assembly, thereby insuring clean oil acting upon the bearings themselves which contributes to the long life of the bearing assembly, enhancing its ability to transmit drilling weight from the drilling string and-stator or housing portion secured thereto and to the drill bit, as well as its ability to resist radial or lateral motion of the motor shaft within the stator or housing.

- A further object of the invention is to provide a bearing assembly in a fluid drilling motor which is capable of safely transmitting greater drilling weights from the drill string and stator or housing to the drill bit. More particularly, a plurality of thrust bearings are used in which one of the bearings normally carries the weight being imposed on the drill bit up to a predetermined amount, an additional bearing being brought into operation to transmit drilling weight to be imposed on the bit in excess of the predetermined amount.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in th drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of iilustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is a side elevational view of the apparatus secured to a string of drill pipe thereabove and to a drill bit therebelow disposed in a bore hole, such as a well bore.

FIGS. 2a, 2b, 2d, 2e, and 2f collectively constitute a quarter-sectional view, parts being shown in side elevation, through the apparatus illustrated in FIG. 1, and on an enlarged scale, FIGS. 2b, 2c, 2d, 2e, and 2f being lower extensions of FIGS. 2a, 2b, 2c, 2d and 2e, respectively.

FIG. 3 is a cross-section taken along the line 33 on FIG. 211,

FIG. 4 is a cross-section taken along the line 4-4 on FIG. 2a;

FIG. 5 is a cross-section taken along the line 5-5 on FIG. 2b; and

FIG. 6 is a vertical section through the dump valve portion of the apparatus disclosed in FIG. 2a, the valve being in its closed position during operation of the drilling motor. A hydraulic downhole apparatus M is illustrated in the drawings, the upper portion of which is connected to a tubular string P, such as a string of drill pipe extending to the top of a bore hole H, such as an oil or gas well being drilled, and the lower end of which is secured to a suitable rotary drill bit A having cutters B for operating upon the bottom C of the bore hole. The drilling apparatus includes an upper hydraulic motor portion 10 and a lower drive shaft portion 11 connected to the rotary drill bit, a universal joint assembly 12 being disposed between the upper and lower portions. As disclosed, an outer housing structure 13 is provided, including an upper sub 14 having a threaded box 15 threadedly secured to the lower pin 16 of an adjacent drill pipe section P, this sub having a lower pin 17 threadedly secured to an outer stator housing 18. The stator housing has mounted therein an elongate elastomer rubber or rubber-like stator 19 having steeply pitched helical lobes or threads 20 coacting with an elongate metallic hollow rotor 21 having steeply pitched helical lobes or threads 22 companion to the stator lobes. Details of the stator and rotor lobes and their coaction are unnecessary to an understanding of the present invention, since they are described in US. Pat. No. 1,892,217. The number of stator lobes 20 is one more than the number of rotor lobes 22. As specifically illustrated, the rubber or elastomer stator has four helical lobes, whereas the metallic rotor has three lobes.

The lower threaded box 23 of the stator housing 18 is threadedly secured to the upper end of an intermediate housing portion 24, the lower pin end 25 of which is threadedly secured to a lower housing portion or section 26 enclosing a bearing assembly 27 extending between the motor shaft 11 and the housing 26, and which has the purpose of resisting radial movement of the drive shaft within the housing structure, and for transmitting drilling weight from the string of drill pipe P through the housing structure 13 to the drill bit A, to force the cutters B against the bottom C of the bore hole.

The hollow rotor 21 has a lower threaded box 28 threadedly secured to the upper end of a rotor extension 29 having side ports 30 establishing communication between a central passage 31 through the rotor extension and a central passage 32 of the rotor which extends to its upper portion, the latter carrying a valve assembly 33.

As shown, a valve seat 34 is threadedly secured within the upper end of the rotor, this seat having lateral slots or openings 35 in its upper portion. A valve or piston member 36 is movable longitudinally within the seat, this piston including an upper valve head 37 slidable along the inner cylindrical seat portion 38 of the seat, the valve head carrying a suitable elastomer or other seal 39 therein adapted to seal against the cylindrical seat 38. The intermediate portion 40 of the piston is reduced in diameter to form an annular passage 41 with the valve seat, the lower portion of thepiston having an outwardly directed flange 42 provided with a plurality of axial ports 43 extending therethrough establishing communication between the annular passage 41 and the central passage 32 through the rotor 21. A helical compression spring 44 has its lower portion bearing against a rotor shoulder 45 and its upper portion against the flange 42 to urge the piston 36 upwardly until the flange 42 engages the lower end 46 of the seat 34, at which time the valve head 37 uncovers a portionof the seat openings 35, permitting fluid to flow between the rotor passage 32 and the upper sub 14 and drill pipe P thereabove (FIG. 2a). When fluid under pressure is being pumped down through the string of drill pipe P, the valve piston 36 is shifted downwardly to an extent limited by the flange 42 engaging an upper rotor shoulder 47 (FIG. 6), at which time the valve head 37 is disposed within the cylindrical valve seat 34 and below the seat openings 35, thereby closing the central rotor passage 32 to the flow of fluid therethrough, the elastomer seal 39 preventing leakage between the cylindrical seat 38 and the valve head 37.

The lower end of the rotor extension 29 is threadedly secured to the upper end of an upper connector 48, the lower end of which is operatively connected to an elongate universal joint assembly 12 of any suitable type. This assembly includes two universal joints and is somewhat inclined to the axis of the rotor, the lower end of the assembly being secured to a lower connector 49 threadedly attached to the upper end of a drive shaft extension 50, which, in turn, is secured to the drive shaft 11 by a spline 50a. The universal joint preferably has an elastic cover 51 suitably secured thereto to prevent the drilling mud or other fluids flowing through the apparatus from entering the universal joint structure and adversely affecting the universal joints and the lubricant normally contained within the cover. A suitable universal joint assembly, including the two universal joints, is manufactured by the Apex Machine and Tool Company, being illustrated in its catalog. Since the rotor 21 partakes of an eccentric or orbital movement around the axis of the stator 19 during its rotation, the universal joint assembly 12 transmits such eccentric motion of the rotor to the motor drive shaft 11,

which is retained in a concentric relation with respect to the housing structure 13.'

The lower portion of the drive shaft 11 is constituted as a bit sub 52 having a lower threaded box 53 threadedly receiving the usual upper pin 54 of the drill bit A, the pin and box being firmly secured to and shouldered against one another, in a known manner; The upper portion of the bit sub 52 has an upwardly facing shoulder 55 through which drilling weight is transmitted from the drill pipe P and housing structure 13 to the hit sub 52 and to the drilling bit Radial and axial thrusts are transmitted through the bearing assembly 27 between the drive shaft 11 and the outer housing structure 13. An upper thrust ring surrounds the lower portion of the drive shaft extension 50, its inner portion overlapping an external flange 61 at the lower end of the extension, the upper surface of the thrust ring engaging a lower thrust shoulder pro I vided by the lower end 63 of the housing member 24, The lower surface of this thrust ring 60 bears against an upper bearing housing member 64, the upper end of which carries an external elastomer side seal 65 sealingly engaging the inner wall of the lower housing member 26, the lower end of the upper bearing housing member being threaded ly secured to a lower bearing housing member 66, the lower end of which is threadedly secured to a terminal bearing housing member 67,

The bearing structure includes an inner upper sleeve 68 around the drive shaft 11, the upper end of which is engaged by a nut'69 threadedon the drive shaft. The lower end of the sleeve 68 bears againstthe inner race 70 of an upper radial bearing 71, of suitable construction, this bearing preferablyincluding roller bearings (not shown), such roller bearings riding against the inner wall of the upper bearing housing an internal flange 72 on the latter extending Qverthe'upper radial bearing 71 to prevent its upward movementwith respect to the housing member 64. This flange has afiller port 73 extending therethrough that can be closed by a plug 74 threaded into the outer portion of theport.

The lower portion of the upper radial bearing 71 rests upon a thrust ring 75 which is engaged by a downwardly facing shoulder 76' provided by the terminus of the upper bearing housing member64, this thrust ring bearing against an axial upperthrust bearing 77. As specifically illustrated, this bearing includes an upper race 78, a lower race 79,and intervening bearingballs 80, the lower race resting upon an upwardlydirected shoulder 81 of the lower bearing housing member 66, the bearing itself surrounding a thrust sleeve 82 extending from the upper radial bearing 71 to a load transmitting ring 83 at its lower end. The lower race 79 of the upper thrust bearing rests upon a thrust ring84 that engages a yield ring85which functions as a-stiff spring. The yield ring including upper and lower portions 86, 87 and an intermediate outwardly bowed portion 88. The lower end of the. yield ring-bears against an external flange 89 on the thrust sleeve -82.' By. way of exam: ple, the yield ring 85 will deflect when subjected to axial loading," but will not take a permanenfset until after a load in excessof a predetermined value; such as 20,000 pounds, has been'imposed'thereonuwhen such load is exceeded, the outerhousing structure 13and lower bearing housing member 66 can move down:

wardly to. a slight extent, so "thata downwardly directed shoulder 90 on the lower bearing housing member 66, which engages a lower thrust ring 91, can force the latter against an intermediate axial thrust bearing 92, including an upper race 93, a lower race 94 and intervening ball bearing elements 95, to engage the lower race 94 with the load transmitting ring 83. This ring engages a thrust sleeve 96 disposed within a lower axial load transmitting bearing 97, the sleeve engaging the inner race 98 of a lower radial bearing 99, the race 98 engaging a lowermost thrust sleeve 100 abutting a ring 101 that engages the bit sub shoulder 55. The lower race 102 of the lowermost axial thrust bearing 97 rests upon a ring 103 which, in turn, rests upon the upper end 104 of a bearing housing member extension 67 that is threadedly secured to the lower bearing housing member 66.

The lower radial bearing 99 transmitting its load from the inner bearing race 98 through roller or corresponding bearings (not shown) to the extension 67, the outer portion of the lower bearing 99 resting upon an upwardlydirected shoulder 105 on the extension. The extension has a downwardly facing shoulder 106 resting upon a companion upwardly facing shoulder 107 on thelower housing member 26, the extension having a fillerpor t 108 extending therethrough closed by a threaded plug 109. The entire bearing assembly can be filled with lubricating oil by removing the upper and lower plugs 74, 109 and injecting the lubricant through the ports 73, 108 and through the entire bearing assembiy 27, this lubricating oil also filling the annular space 110 between the upper sleeve 68 and upper bearing housing member 64, as described hereinbelow. The plugs 74, 109 are then replaced to close the ports 73, 108.

The drilling mud, or other liquid externally of the bearing assembly 27, is prevented from entering the bearing structure. The upper sleeve 68 has a side seal ll l 'sealingly engaging the periphery of the drive shaft 11 the lowermost sleeve 100 also having an internal elastomer seal '112 engaging the periphery of the drive shaft. This lowermost sleeve rotates with the drive shaft 11,'there being a rotating seal mounted in the lower bearing extension67, including an'inner seal member 113 engaging the periphery of the lower sleeve backed by an elastomer sealring 114. The external'pressure is transmitted to the oil in the bearing structure by an an nular booster piston 115 disposed in the annular space ll0between the upper sleeve and the upper bearing housing member. This annular piston has a lower seal ring 116 engaging the inner wall of the upper bearing housing member 64 and an upper seal ring 117 engaging the inner wall 118 of the upper bearing housing member 64, this latter wall having a slightly greater internal diameter than the internal diameter of the upper bearing housing member engaged by t the lower seal 116, an internal seal 119 bearing against the periphery of the upper sleeve 68 to permit the upper sleeve to rotate with respect thereto.

Eluid pressure acts downwardlyover the annular boosterpiston'llS over the area S between the internal and externalseals 119, 117 to force the piston downwardly against the body of oil in the annular bearing space 110. The lower portion of the annular piston has an area'R smaller than the area S between the internal Sear 119 and the lower seal 116 exerting its force against the oil, or other lubricant, in the bearing assembly. Thus, the annular piston 115 functions as a booster, the total pressure exerted on its upper portion acts over a smaller area R of the lower portion to impart a greater unit pressure to the oil in the bearing assembly. It is to be noted that a bleeder port 120 is provided through the upper bearing housing member 64 between the upper and lower seals 117, 116 and a bleeder port 121 is also provided through the lower housing 26 communicating with the other port 120 to prevent entrapment of any fluid between the upper and lower seals.

In the use of the apparatus, the drill bit A is secured to the lower end of the drive shaft 11 and the upper sub 14 is threadedly secured to the lower end of the string of drill pipe P through which the apparatus is lowered through the drilling mud in the bore hole H to the bottom C thereof. During the lowering movement, the dump valve 33 is in its open position, as illustrated in FIG. 2a, which permits fluid to flow upwardly through the usual jets or nozzles (not shown) in the drill bit into its central passage 122, through the drive shaft passage 123, and into its extension 50, from where the fluid flows outwardly through the side ports 124 into the annular space 125 above the bearing assembly and between the housing structure 13 and the drive shaft extension 50, lower connector 49, universal joint assembly 51 and the rotor extension 29, the annular space communicating with the lower end of the elastomer or rubber stator 19. This fluid can continue flow inwardly through the side ports 30 into the central passage 31 of the rotor extension 29, from where it flows upwardly through the passage 32 of the hollow rotor 21 and through the ports 43 in the valve flange 42 into the annular space 41 between the valve piston 36 and the cylindrical seat 34, the fluid then flowing outwardly through the openings 35 in the upper portion of the seat, and into the upper sub 14 for continued flow in an upward direction through the drill pipe P.

Because of the presence of the drilling motor at the lower end of the drill pipe P, it is not necessary to rotate the string of drill pipe and the outer housing structure 13, which are actually held stationary at the top of the well bore. Drilling mud or other fluid is pumped down through the drill pipe P and into the upper sub 14, the pressure of the fluid forcing the valve piston 36 downwardly to close the upper openings 35, as illustrated in FIG. 6. This closes the rotor passage 32, requiring the drilling mud to flow through the spaces formed between the rotor 21 and rubber stator 19, such fluid passing axially along the stator and rotor and causing the rotor to rotate, fluid continuing to flow downwardly until it discharges from the lower end of the elastomer stator into the annular space 125. From the annular space,the drilling mud, or other fluid, passes through the side ports 124 of the shaft extension 50 into the shaft passageway 123, flowing from such passageway into the drill bit passageway 122 and discharging from its nozzles (not shown) against the cutters B and toward the bottom C of the bore hole, for the purpose of cleaning the cutters and flushing the cuttings in a lateral outward direction and upwardly through the annular space in the well bore surrounding the drill bit and the apparatus M, effecting drilling of the hole and the removal of the cuttings therefrom to the top of the bore hole H.

During the drilling action, an appropriate drilling weight is imposed on the drill bit A by allowing a portion of the weight of the drill pipe P to rest upon the housing structure 13. This drilling weight is transmitted from the housing structure through the upper thrust ring 60 to the upper bearing housing member 64, and from its lower shoulder 76 through the thrust ring to the upper axial thrust bearing 77, from Where it is transferred through the thrust ring 84 to the yield ring 85 and to the flange 89 of the thrust sleeve 82, which bears against the load transmitting ring 83. This ring bears against the thrust sleeve 96, the downward thrust or load being transferred therefrom through the inner race 98 of the lower bearing and through the lower thrust sleeve 100 and ring 101 to the bit sub shoulder 55. The drilling weight or force is then transmitted through the bit sub 52 to the drilling bit A to force its cutters B against and into the bottom C of the bore hole H.

It will be noted that so long as the drilling weight imposed on the bit does not exceed the load transmitting capacity of the yield ring 85 before it begins taking a permanent set, the drilling load is being transferred through the upper thrust bearing 77 only, the initial distance between the intermediate thrust ring 91 and the load transmitting ring 83 being greater than the axial extent of the intermediate bearing 92. When the predetermined load transmitting capacity of the yield ring 85 reaches a value at which it commences taking a permanent set, the intermediate axial thrust bearing 92 is engaged by both the lower thrust ring 91 and the load transmitting ring 83, whereupon a certain portion of the drilling weight is transferred from the shoulder 90 of the lower bearing housing member 66 to the lower ring 91 and through the intermediate bearing structure 92 to the load transmitting ring 83, this bearing 92 then transmitting its portion of the axial thrust or drilling weight in parallel with the load that is being transmitted through the upper axial thrust bearing 77. The intermediate thrust bearing 92 will transfer the additional load that exceeds the load at which the yield ring 85 commences taking a permanent set. Accordingly, both axial bearings 77, 92 are dividing the load, which prevents the bearings from being overloaded and contributes to their greatly extended life, and the effective drilling life of the drilling motor itself. While the drive shaft 11 is being rotated by the rotor 21 at the required speed, the radial bearings 71, 99 are preventing the drive shaft from shifting laterally within the housing structure 13, retaining it coaxial therewith.

1n the event the drill bit A is lifted from the bottom C of the bore hole while fluid is being pumped through the drilling motor 10, and the rotor 21, universal joint 12, drive shaft 11 and bit A are rotated, the load transmitting ring 83 will rest upon the lowermost axial bearing 97 to support the downward thrust imparted on the rotor by the drilling fluid exerting against its lobes 22, and the weight of the bit drive shaft 11 and the universal joint 12 thereabove. This load is transferred through the lower thrust ring 103 to the upper end 104 of the bearing sub 67.

All of the bearing parts are immersed in the bath of oil extending from the lower fill port 108 up to the annular booster piston 115. The pressure of the drilling mud is being imposed upon the annular booster piston 115, exerting its force against the oil in the bearing section, the unit pressure exerted against the oil in the bearing section always beinghigher than the pressure externally thereof, because of the fact that the area S of the upper portion of the annular piston is greater drilling mud or foreign fluids from entering the bearing.

section and contaminating the oil, resulting in damage to any of the bearing parts.

When the apparatus is to be removed from the bore hole, the pumping of fluid down through the drill string ceases, relieving the pressure on the drilling motor and the force holding the valve piston 36 in its closed position (FIG. 6), the spring 44 shifting the piston to its open position (FIG. 2a). Fluid can drain from the drill pipe P, flowing downwardly through the openings 35, annular passage 41, hollow rotor passage 32, and the side ports 30 into the annulus 125, from where the liquid drains through the lower extension ports 124 into the hollow drive shaft passage 123 and the drill bit passage 122, exiting through its nozzle or jets into the well bore l-l. Thus, the drill pipe P automatically drains while the apparatus is being elevated in the bore hole to be removed at its surface, preventing the pulling of a wet string; that is, preventing the drilling mud from overflowing at the top of the bore hole onto the rig floor, wetting the equipment and personnel.

As was pointed out above, for a given pressure differ ential of the drilling fluid being pumped through the drilling motor when drilling is taking place, the torque generated through use of the three lobe rotor is about one and three-fourths times as great as prior drilling motors of the Moineau type that use a single lobe rotor only. The fluid drilling motor illustrated can be operated at at least twice the pressure differential of the prior drilling motors, which means that twice as much hydraulic horsepower can be applied to the motor. This fact, coupled with the ability to develop a torque of about one and three-fourths times as great as the prior drilling motor at any given pressure, results in the present motor being capable of generating at least three and one-half times the torque of the prior drilling motors. While drilling, because of such much greater torque, the motor has the capability of permitting approximately three and one-half times as much drilling weight to be imposed on the bit, as compared to prior drilling motors.

The present drilling motor also rotates at a much slower speed than prior drilling motors, with the pumping of drilling fluid at the same volumetric rate and at the same differential pressure through the motor. By way of example, pumping at a rate of 350 gallons per minute at a differential pressure of 225 p.s.i., results in the prior drilling motor rotating at about 400 r.p.m.; whereas the present drilling motor operating under the same conditions rotates at approximately 280 r.p.m. This permits drilling bits, designed to operate at slower speed, to be used effectively with the present drilling motor. It also results in a decrease in the amount of vibration developed by the rotor, and this decrease in vibration is further enhanced by the fact that the rotor is hollow, having a much smaller mass than if it were solid. The use of the hollow rotor enables the dump valve 33 to be built into the rotor itself, permitting appropriate drainage of the drill pipe P while coming out of the hole, and automatic filling of the drill pipe as the apparatus is being run in the hole.

It is apparent that a drilling motor has been provided having a much longer life than prior drilling motors, capable of developing a much higher torque, and permitting a greater drilling weight to be imposed upon the drill bit, if required. The longer life is in part attributable to the slower rotating speed of the motor and to the bearing assembly, which is sealed against entry of foreign matter thereinto that would contaminate the lubricant, producing damage to the bearing parts. Thus, the drilling motor is capable of staying at the bottom of'the bore hole a longer time, since the drill bit rotating at a slower speed lasts longer, the increased life of the drilling motor itself making it unnecessary to prematurely pull the apparatus and drilling bit out of the hole.

I claim:

1. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said'housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions above and below said stator; and means carried by and rotatable with said rotor for selectively opening and closing said rotor passage.

2. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for bypassing fluid through said rotor passage between housing structure regions above and below said stator; valve means'carried by and rotatable with said rotor responsive to the pressure of fluid pumped down the drilling string for closing said rotor passage; and means on said rotor for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.

3. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; wherein said stator has four lobes, said rotor having three lobes; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions above and below said stator; and means carried by and rotatable with said rotor for selectively opening and closing said rotor passage.

4. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; wherein said stator has four lobes, said rotor having three lobes; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions above and below said stator; valve means carried by and rotatable with said rotor responsive to the pressure of fluid pumped down the drilling string for closing said rotor passage; and means on said rotor for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.

5. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between said shaft means and housing struc ture; axial bearing means between said shaft means and housing structure for transmitting axial loads between said housing structure and shaft means; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained, and booster piston means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space, said booster piston means having a first effective transverse area responsive to the pressure of fluid externally of said confined space, said booster piston means also having a second effective transverse area bearing against the lubricant in said confined space which is less than said first transverse area.

6. Apparatus as defined in claim 5; said confined space being an annular space between said shaft means and housing structure, said booster piston means defining an end of said annular space and comprising an annular piston having said second effective transverse area bearing against the lubricant and said first effective transverse area subject to the pressure of the fluid externally of said annular space.

7. Apparatus as defined in claim 5; said stator and rotor having coengaging means to provide a positive displacement hydraulic motor wherein said rotor is rotated in response to fluid under pressure pumped down the drilling string and between said rotor and stator; said rotor having passage means including upper and lower openings for by-passing fluid through said passage menas between housing structure regions above and below said stator; means on said rotor for selectively opening and closing said passage means; said shaft means having a fluid passage adapted to receive fluid from said lower opening for discharge into the drill bit.

8. Apparatus as defined in claim 5; said stator and rotor having coengaging means to provide a positive displacement hydraulic motor wherein said rotor is rotated in response to fluid under pressure pumped down the drilling string and between said rotor and stator; said rotor having passage means including upper and lower openings for by-passing fluid through said passage means between housing structure regions above and below said stator; means on said rotor for selectively opening and closing said passage means; said shaft means having a fluid passage adapted to receive fluid from said lower opening for discharge into the drill bit; said means on said rotor comprising valve means responsive to the pressure of fluid pumped down the drilling string for closing said passage means, and spring means acting between said rotor and valve means for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.

9. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between said shaft means and housing structure; axial bearing means between said shaft means and housing structure for transmitting axial loads between said housing structure and shaft means; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster piston means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster piston means defining an end of said annular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space, said second portion having a greater transverse pressure responsive annular area than the transverse annular area of said first portion.

10. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between said shaft means and housing structure; said shaft means having a lower thrust shoulder; a first thrust shoulder on said housing structure; first thrust bearing means engaging said first shoulder; a second thrust shoulder on said housing structure; second thrust bearing means engaging said second shoulder; yieldable means engaging said first bearing means; load transmitting means engaging said yieldable means and lower shoulder to transmit drilling weight from said housing structure through said first shoulder, first bearing means and yieldable means to said lower shoulder; said second bearing means being initially ineffective to transmit drilling weight to said load transmitting means and becoming effective to transmit drilling weight to said load transmitting means upon predetermined yielding of said yieldable means when subjected to a load exceeding a predetermined value.

11. Apparatus as defined in claim and a third thrust bearing between said housing structure and shaft means for axially supporting said shaft means from said housing structure. I

12. Apparatus as defined in claim 10; said yieldable means comprising a yieldable ring adapted to deflect when subjected to axial loads.

13. Apparatus as defined in claim 10; and a third thrust bearing between said housing structure and shaft means for axially supporting said shaft means from said housing structure; said yieldable means comprising a yieldable ring adapted to deflect when subjected to axial loads.

14. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space.

15. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster means defining an end of said annular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space. r

16. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster means for subjecting the liquid lubricant to a greater un'it pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster means defining an end of saidannular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space, said second portion having a greater transverse pressure responsive annular area than the annular area of said firstportion.

(5/69) I r 1" rw u "w r GER 1 11 lCAl 12 O1 QORRILC l lON Patent; No. 3,840,080 I Dated bctober 8, 1974 JInventofls) LL- 1AM 0. BERRYMAN It iS certified that error appears in the above-identified patent and that said Letters. Patent are helqeby correcvted as ghox m below:

Column 1, .li-ne- .chaqge Y'mVingf' to ,--remqv i,.ng Colgmn line 17 I before 2d" in1t -=-2c line 32;. sente'nce begi-l ming with "A hyd'r aulic I A c lwfih o'l e aPPQf'tUs fM start.=a

I new par agraph I Cblflmn 8, 1in e 67 after "annular" ihseft; bpo.ste r CO1@ 12 line 37: char 1ge Y'merias" tio -means sign'e d an d .seal ed this 7th day of January} 1975.

(SE-AL) Att'eStp Mcconfl. GIBSON R; cLMARsHAiL-DANN Attestlng O ffiger Commissioner of Patents 

1. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions above and below said stator; and means carried by and rotatable with said rotor for selectively opening and closing said rotor passage.
 2. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for bypassing fluid through said rotor passage between housing structure regions above and below said stator; valve means carried by and rotatable with said rotor responsive to the pressure of fluid pumped down the drilling string for closing said rotor passage; and means on said rotor for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.
 3. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; wherein said stator has four lobes, said rotor having three lobes; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions above and below said stator; and means carried by and rotatable with said rotor for selectively opening and closing said rotor passage.
 4. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; said stator and rotor having coacting helical lobes constantly in contact with one another and in any transverse section, whereby fluid pumped downwardly through the drilling string passes through the helical passages between said stator and rotor lobes to rotate said rotor in an orbital path around the axis of the stator; said rotor being hollow throughout a major portion of its length and having a plurality of helical lobes, said stator having one more helical lobe than said rotor; a drive shaft rotatably supported in said housing structure below said rotor and having lower connector means for attachment to a drill bit, said shaft having passage means for conducting fluid discharging from said stator to the drill bit when attached to said lower connector means; and means interconnecting said rotor and drive shaft for transmitting the rotary motion of said rotor to said drive shaft; wherein said stator has four lobes, said rotor having three lobes; said hollow rotor providing a central passage therein; said rotor having upper and lower openings communicating with said passage for by-passing fluid through said rotor passage between housing structure regions abOve and below said stator; valve means carried by and rotatable with said rotor responsive to the pressure of fluid pumped down the drilling string for closing said rotor passage; and means on said rotor for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.
 5. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between said shaft means and housing structure; axial bearing means between said shaft means and housing structure for transmitting axial loads between said housing structure and shaft means; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained, and booster piston means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space, said booster piston means having a first effective transverse area responsive to the pressure of fluid externally of said confined space, said booster piston means also having a second effective transverse area bearing against the lubricant in said confined space which is less than said first transverse area.
 6. Apparatus as defined in claim 5; said confined space being an annular space between said shaft means and housing structure, said booster piston means defining an end of said annular space and comprising an annular piston having said second effective transverse area bearing against the lubricant and said first effective transverse area subject to the pressure of the fluid externally of said annular space.
 7. Apparatus as defined in claim 5; said stator and rotor having coengaging means to provide a positive displacement hydraulic motor wherein said rotor is rotated in response to fluid under pressure pumped down the drilling string and between said rotor and stator; said rotor having passage means including upper and lower openings for by-passing fluid through said passage menas between housing structure regions above and below said stator; means on said rotor for selectively opening and closing said passage means; said shaft means having a fluid passage adapted to receive fluid from said lower opening for discharge into the drill bit.
 8. Apparatus as defined in claim 5; said stator and rotor having coengaging means to provide a positive displacement hydraulic motor wherein said rotor is rotated in response to fluid under pressure pumped down the drilling string and between said rotor and stator; said rotor having passage means including upper and lower openings for by-passing fluid through said passage means between housing structure regions above and below said stator; means on said rotor for selectively opening and closing said passage means; said shaft means having a fluid passage adapted to receive fluid from said lower opening for discharge into the drill bit; said means on said rotor comprising valve means responsive to the pressure of fluid pumped down the drilling string for closing said passage means, and spring means acting between said rotor and valve means for shifting said valve means to open position in the absence of fluid pressure pumped down the drilling string.
 9. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between saId shaft means and housing structure; axial bearing means between said shaft means and housing structure for transmitting axial loads between said housing structure and shaft means; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster piston means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster piston means defining an end of said annular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space, said second portion having a greater transverse pressure responsive annular area than the transverse annular area of said first portion.
 10. Fluid motor apparatus for drilling a bore hole in a formation: a housing structure having upper connector means for attachment to a tubular drilling string extending to the top of the bore hole, said structure including a stator; a rotor within said stator; shaft means connected to said rotor for attachment to a drill bit to rotate the same; radial bearing means between said shaft means and housing structure for transmitting radial forces between said shaft means and housing structure; said shaft means having a lower thrust shoulder; a first thrust shoulder on said housing structure; first thrust bearing means engaging said first shoulder; a second thrust shoulder on said housing structure; second thrust bearing means engaging said second shoulder; yieldable means engaging said first bearing means; load transmitting means engaging said yieldable means and lower shoulder to transmit drilling weight from said housing structure through said first shoulder, first bearing means and yieldable means to said lower shoulder; said second bearing means being initially ineffective to transmit drilling weight to said load transmitting means and becoming effective to transmit drilling weight to said load transmitting means upon predetermined yielding of said yieldable means when subjected to a load exceeding a predetermined value.
 11. Apparatus as defined in claim 10; and a third thrust bearing between said housing structure and shaft means for axially supporting said shaft means from said housing structure.
 12. Apparatus as defined in claim 10; said yieldable means comprising a yieldable ring adapted to deflect when subjected to axial loads.
 13. Apparatus as defined in claim 10; and a third thrust bearing between said housing structure and shaft means for axially supporting said shaft means from said housing structure; said yieldable means comprising a yieldable ring adapted to deflect when subjected to axial loads.
 14. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space.
 15. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearing means are contained; and booster means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster means defining an end of said annular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space.
 16. Apparatus as defined in claim 10; means providing a confined space adapted to contain a liquid lubricant and in which said radial bearing means and axial bearIng means are contained; and booster means for subjecting the liquid lubricant to a greater unit pressure than the unit pressure externally of said confined space; said confined space being an annular space between said shaft means and housing structure, said booster means defining an end of said annular space and comprising an annular piston having a first portion bearing against the lubricant and a second portion subject to the pressure of the fluid externally of said annular space, said second portion having a greater transverse pressure responsive annular area than the annular area of said first portion. 